Angiogenesis
Angiogenesis is the process in which new blood vessels grow into an area which lacks a sufficient blood supply. Angiogenesis commences with the erosion of the basement membrane surrounding endothelial cells and pericytes forming capillary blood vessels. Erosion of the basement membrane is triggered by enzymes released by endothelial cells and leukocytes. The endothelial cells then migrate through the eroded basement membrane when induced by angiogenic stimulants. The migrating cells form a "sprout" off the parent blood vessel. The migrating endothelial cells proliferate, and the sprouts merge to form capillary loops, thus forming a new blood vessel.
Angiogenesis can occur under certain normal conditions in mammals such as in wound healing, in fetal and embryonic development, and in the formation of the corpus luteum, endometrium and placenta. Angiogenesis also occurs in certain disease states such as in tumor formation and expansion, or in the retina of patients with certain ocular disorders. Angiogenesis can also occur in a rheumatoid joint, hastening joint destruction by allowing an influx of leukocytes with subsequent release of inflammatory mediators.
The evidence for the role of angiogenesis in tumor growth was extensively reviewed and present by O'Reilly and Folkman in U.S. Pat. No. 5,639,725, the entire disclosure of which is incorporated herein by reference. It is now generally accepted that the growth of tumors is critically dependent upon this process.
High Molecular Weight Kininogen
High molecular weight kininogen (HK) is a 120 kD glycoprotein containing heavy and light chains, composed of domains 1 through 3, and 5 and 6, respectively. This form of HK is often referred to as "single-chain high molecular weight kininogen". HK binds with high affinity to endothelial cells, where it is cleaved by plasma kallikrein into heavy and light chains. This form of cleaved HK is known as "two-chain high molecular weight kininogen" (HK.sub.a). The heavy and light chains are linked by domain 4 in intact HK; domain 4 contains bradykinin, a potent biologically active nonapeptide. Bradykinin is released from HK through cleavage mediated by plasma kallikrein (Kaplan et al., Blood 70:1-15, 1987). The heavy and light chains resulting from the elimination of bradykinin remain linked by a disulfide bond between cysteine residues at positions 10 and 596. Conversion of HK to HK.sub.a is accompanied by a dramatic structural rearrangement. The central globular region of HK is separated after bradykinin liberation and rearranged with cysteine protease inhibitory regions opposite the prekallikrein binding region (Weisel et al., J. Biol. Chem. 262:1405, 1987).
The HK light chain consists of the following sequence of HK amino acids 372-626 (SEQ ID NO:1): EQU SSRIGEIKEETTVSPPHTSMAPAQDEERD SGKEQGHTRRHDWGHEKQRKHNLGHGH KHERDQGHGHQRGHGLGHGHEQQHGLG HGHKFKLDDDLEHQGGHVLDHGHKHKH GHGHGKHKNKGKKNGKHNGWKTEHLAS SSEDSTTPSAQTQEKTEGPTPIPSLAKPG VTVTFSDFQDSDLIATMMPPISPAPIQSD DDWIPDIQTDPNGLSFNPISDFPDTTSPK CPGRPWKSVSEINPTTQMKESYYFDLTD GLS (SEQ ID NO:1).
The HK light chain consists of HK amino acids serine-372 to threonine 383, forming the C-terminal portion of HK domain 4 remaining after bradykinin liberation; HK amino acids valine 384 to lysine 502, forming the HK domain 5 (D5); and HK amino acids threonine 503 to serine 626, forming the HK domain 6 (D6). D5 is rich in histidines, glycines and lysines and has been postulated to be involved in binding to negatively charged surfaces. D5 serves as a cell binding site on platelets, granulocytes and endothelial cells. For a recent review including a discussion of HK's domain structure, and the functional significance of the various domains (including D5), see Colman and Schmaier, Blood 90:3819-3843 (1997). HK.sub.a has been shown to bind to the urokinase receptor (uPAR) on endothelial cells (Colman et al., J. Clin. Invest. 100:1481-7 (1997). HK D5 has been shown to participate in cell binding; certain peptides from regions of D5 have been found to inhibit HK binding to endothelial cells (Hasan et al., J. Biol. Chem., 270:19256, 1995). Despite these findings, no role has been suggested for HK in the process of angiogenesis.